refactor(DP15): centralize sendStateEvent as-any cast in typed helper

Add a typed `sendStateEvent(mx, roomId, eventType, content, stateKey?)`
helper in utils/room.ts that mirrors the DP16 account-data helper pattern.
The SDK's typed `sendStateEvent` overload rejects the fork's custom
`StateEvent` enum values, so every call site cast arg 2 to `any` (which
also collapsed the content type). The single `as any` cast now lives inside
the helper; a generic `content: T extends object` keeps each call site's
content type checked.

Route all 32 `mx.sendStateEvent(..., StateEvent.X as any, ...)` casts across
20 files through the helper. The 2 dynamic-string casts in developer-tools
(SendRoomEvent, StateEventEditor) pass a runtime string, not an enum value,
so they stay as-is.

No behavior change.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/features/add-existing/AddExisting.tsx

@@ -38,7 +38,7 @@ import { mDirectAtom } from '../../state/mDirectList';
 import { roomToParentsAtom } from '../../state/room/roomToParents';
 import { useAllJoinedRoomsSet, useGetRoom } from '../../hooks/useGetRoom';
 import { VirtualTile } from '../../components/virtualizer';
-import { getDirectRoomAvatarUrl, getRoomAvatarUrl } from '../../utils/room';
+import { getDirectRoomAvatarUrl, getRoomAvatarUrl, sendStateEvent } from '../../utils/room';
 import { RoomAvatar, RoomIcon } from '../../components/room-avatar';
 import { nameInitials } from '../../utils/common';
 import { useMediaAuthentication } from '../../hooks/useMediaAuthentication';
@@ -136,9 +136,10 @@ export function AddExistingModal({ parentId, space, requestClose }: AddExistingM
         await rateLimitedActions(selectedRooms, async (room) => {
           const via = getViaServers(room);
 
-          await mx.sendStateEvent(
+          await sendStateEvent(
+            mx,
             parentId,
-            StateEvent.SpaceChild as any,
+            StateEvent.SpaceChild,
             {
               auto_join: false,
               suggested: false,